Methamphetamine (METH) causes long-term damage to dopaminergic neurons, with adolescent being less susceptible than young adult rats. Further, pretreatment with METH, beginning in adolescence, prevents the persistent dopaminergic deficits caused when METH is administered during adulthood. Mechanisms underlying these "resistance" phenomena remain to be elucidated. One overarching hypothesis of this program project is that events occurring during the early hours (i.e., <8 h) after treatment (a period referred to herein as "stage 1") and later (i.e., 24 - 72 h after treatment, referred to herein as "stage 2") are both necessary to elicit this damage. Thus, this project will test the hypothesis that "stage 2" events related to intracellular DA management are critical for the persistent dopaminergic deficits caused by METH, and that these events are absent in both adolescent rats and those treated with METH during development." This will be tested by investigating: 1) the impact of development, and of METH treatment during adolescence, on the expression of METH-induced effects occurring during "stage 2" including disruption of factors regulating intraneuronal DA distribution and reactive species formation. For completeness, glial cell activation will be assessed as well. 2) if targeted inhibition of "stage 2" events prevents the persistent dopaminergic deficits caused by METH. Pharmacological manipulations will be performed after the onset of "stage 1" to determine if these treatments prevent "stage 2" events and/or the long-term dopaminergic damage caused by METH. 3) the impact of development, and of METH treatment during adolescence, on the expression of METH-induced effects occurring during "stage 1" including effects on: 1) the vesicular monoamine transporter-2;2) the DA transporter and 3) reactive species formation. This will be accomplished even though the focus of this Project is "stage 2," as it is hypothesized that the factors occurring in "stage 1" contribute to its expression. Importantly, several other factors contribute to the long-term deficits caused by METH and are focuses of other projects in this PO1 application. This Project will focus on specific "stage 1" and "stage 2" factors including those delineated above. Resulting data will be used to inform studies in Projects #2 and #3 regarding potential targets of study, and visa versa. Identification of similar and dissimilar mechanistic factors among the projects will provide insight into not only issues related to METH-induced neurotoxicity, but also degenerative disorders involving dopaminergic neurons such as Parkinson's disease.